Can we find on the instruments the outside air temperature?if yes, where thanksbernard

its the TAT reading on the engine screen right above the number 1 N1 gauge

i m surprised by this value tat -15°c @ 37000ft if it's the outside air temperature the value is hot for this FL!

TAT is different to SAT, SAT at that altitude would be -56.5C if ISA conditions prevailed, as above 36,090ft, temperature remains constant. Edit: Okay, that's slightly generalised, the tropopause is at different altitudes at different degrees of latitude, but that is the average level, and the least complicated way of explaining it.

Edited August 7, 201114 yr by Rónán O Cadhain

TAT takes into account the friction on the temperature probe as the aircraft moves through the air. SAT (same as OAT) can be found in the PROG section, one or two pages in.

yep i've found OAT is readable on the fmc on the perf pagei search about temperature because of the message TAI ON above 10 degrees , i don't know if it' SAT TAT OAT

Use TAT for determining if A/I is needed.

ok thanks

When you are on the ground, TAT and SAT should read the same. Once the aircraft is flying, the two temperatures start to diverge, with TAT always being the warmer of the two.The faster the aircraft moves through the air, the larger the difference between TAT and SAT.On the Concorde, the TAT would rise to well over 100 degrees C when the aircraft reached its Mach 2 cruising speed... hot enough to boil. water!That can never happen on a subsonic jet aircraft, but in any case, cruise performance, anti-ice requirements, fuel temp etc are all referenced to TAT rather than SAT.

Not trying to nitpick here, but I'm pretty sure it's rather compression than friction. Just FYI.

Fun topic. Just glancing through my books, I find: TAI on

1. =< +10 OAT on the ground (ATIS)
2. =< +10 TAT in flight (Engine display)

TAI off

1. > +10 TAT in flight (Engine display)
2. < -40 SAT in flight (PROG 2) (Climb or Cruise)

So, taxiing around, if the ATIS is calling 10C and moisture, TAI on.On departure, if TAT is 10C or less + moisture TAI on.Climb and cruise, you have to check the PROG 2/4 page to check the SAT is less than -40C, or no moisture.

TAI off

1. > +10 TAT in flight
2. < -40 SAT in flight (Climb and Cruise)

That's because at less than -40c the ice wont gel to the airframe.

Use TAT for determining if A/I is needed.

Use TAT, OAT, and SAT according to the folks at Boeing.

That's because at less than -40c the ice wont gel to the airframe.

That sounds good to me. Looks like I need to crack the meteorology books again.